Dear Peter,
the beauty of WordPress is that content, settings, and templates are completely separated – text, images, etc added by you are stored in separate folders, the settings are stored in SQL databases, while the template files are stored in their own directories. Updating a theme implies rewriting its template files, and is thus similar in effect with switching to another theme. In both cases, all content and settings remain intact; the only things that may get lost are any changes you’ve made to the template files (the files situated inside the /wp-content/themes/Sensei/ directory).
Sincerely,
Andrew | Satori